Offshore liquefaction process without compression

ABSTRACT

A process for producing liquid oxygen, including an offshore platform the system including cooling a high-pressure nitrogen gas stream in a main heat exchanger, thereby producing a cooled high-pressure nitrogen gas stream, expanding the cooled high-pressure nitrogen gas stream in a turbo-expander, thereby producing a cold low-pressure nitrogen gas stream, warming the cold low-pressure nitrogen gas stream by indirect heat exchange with a high-pressure gaseous oxygen stream, thereby producing a liquefied oxygen stream and a warm low-pressure nitrogen gas stream, wherein, at least a portion of the warm low-pressure nitrogen gas stream is vented to the atmosphere.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. § 119 (a) and (b) to U.S. Provisional Patent Application No. 63/084,701, filed Sep. 29, 2020, the entire contents of which are incorporated herein by reference.

BACKGROUND

In many instances it is desirable to perform rocket launches from offshore platforms to provide sufficient blast buffer distance from populated areas. Additionally, it is preferable from an energy standpoint, to launch rockets near the equator, for the additional boost provided by the Earth's rotation. Countries located in high latitudes, such as Russia, can accomplish this by launching from an offshore platform. If a country has few available launch sites, that do not impact civilian safety, such as China, offshore platform launches are also attractive.

It is desirable for offshore launch platforms to be self-contained. As some rockets require liquid oxygen as a liquid fuel, these platforms may house liquefaction facilities. These facilities will require either large electric motors, or turbine to drive the refrigeration equipment. Such large electrical systems as well as supplying electricity to such systems is prohibitive. In addition, power generating turbines may be gas turbines or steam turbines, which require a combustion boiler. The safety risk of having these potential ignition sources in such close proximity to liquid oxygen and liquid fuel storage is significant.

There is a need in the industry for an offshore platform that can provide the liquefaction of fuel and oxygen without the associated potential ignition risk.

SUMMARY

A process for producing liquid oxygen, including an offshore platform the system including cooling a high-pressure nitrogen gas stream in a main heat exchanger, thereby producing a cooled high-pressure nitrogen gas stream, expanding the cooled high-pressure nitrogen gas stream in a turbo-expander, thereby producing a cold low-pressure nitrogen gas stream, warming the cold low-pressure nitrogen gas stream by indirect heat exchange with a high-pressure gaseous oxygen stream, thereby producing a liquefied oxygen stream and a warm low-pressure nitrogen gas stream, wherein, at least a portion of the warm low-pressure nitrogen gas stream is vented to the atmosphere.

BRIEF DESCRIPTION OF THE FIGURES

For a further understanding of the nature and objects for the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein:

FIG. 1 is a schematic representation of an offshore liquefaction, without compression, in accordance with one embodiment of the present invention.

FIG. 2 is a schematic representation of one embodiment of a liquefying heat exchanger, in accordance with one embodiment of the present invention.

FIG. 3 is a schematic representation of another embodiment of a liquefying heat exchanger, in accordance with one embodiment of the present invention.

FIG. 4 is a schematic representation of one non-limiting embodiment of an air separation unit with liquid oxygen pumping, in accordance with one embodiment of the present invention.

ELEMENT NUMBERS

-   -   101=air feed stream     -   102=air separation unit     -   103=high-pressure gaseous nitrogen     -   104=first portion (of high-pressure gaseous nitrogen)     -   105=second portion (of high-pressure gaseous nitrogen)     -   106=high-pressure gaseous oxygen     -   107=first portion (of high-pressure gaseous oxygen)     -   108=second portion (of high-pressure gaseous oxygen)     -   109=natural gas feed stream     -   110=first portion (of natural gas feed stream)     -   111=second portion (of natural gas feed stream)     -   112=first liquefying heat exchanger     -   113=second liquefying heat exchanger     -   114=first liquefied nitrogen stream     -   115=second liquefied nitrogen stream     -   116=combined liquefied nitrogen stream     -   117=liquefied nitrogen storage     -   118=first liquefied oxygen stream     -   119=second liquefied oxygen stream     -   120=combined liquefied oxygen stream     -   121=liquefied oxygen storage     -   122=first liquefied natural gas stream     -   123=second liquefied natural gas stream     -   124=combined liquefied natural gas stream     -   125=liquefied natural gas storage     -   126=first nitrogen vent stream     -   127=second nitrogen vent stream     -   128=third nitrogen vent stream     -   129=fourth nitrogen vent steam     -   201=cooled high-pressure nitrogen stream     -   202=high-pressure nitrogen expansion turbine     -   203=low-pressure nitrogen stream     -   301=cooled first fraction     -   302=cooled second fraction     -   303=first high-pressure nitrogen expansion turbine     -   304=first low-pressure nitrogen stream     -   305=warmed first low-pressure nitrogen stream     -   306=nitrogen compressor     -   307=hot compressed nitrogen stream     -   308=nitrogen after-cooler     -   309=cooled compressed nitrogen stream     -   310=expansion valve     -   311=two-phase nitrogen stream     -   312=phase separator     -   313=liquid stream (from phase separator)     -   314=vapor stream (from phase separator)     -   315=warmed liquid stream     -   316=cold compressed nitrogen stream     -   317=second high-pressure nitrogen expansion turbine     -   318=second low-pressure nitrogen stream     -   319=combined waste nitrogen stream     -   401=inlet air stream     -   402=cool inlet air stream     -   403=cold booster     -   404=compressed cool feed air stream     -   405=first branch     -   406=second branch     -   407=expander     -   408=expanded feed air stream     -   409=air separation unit column     -   410=liquid oxygen stream     -   411=main heat exchanger     -   412=high-pressure gaseous oxygen stream

DESCRIPTION OF PREFERRED EMBODIMENTS

Illustrative embodiments of the invention are described below. While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

Turning to FIG. 1, an overview of the present invention is provided. Note, FIG. 1 and the following process description describe a two-train liquefaction system. One of ordinary skill in the art will recognize that, depending on the demands of the particular installation, a single train system or a system with more than 2 trains may be utilized, and the following description will still apply.

Air fed stream 101 is provided to air separation unit 102, which thereby produces high-pressure gaseous nitrogen stream 103 and high-pressure gaseous oxygen stream 106. High-pressure gaseous nitrogen stream 103 is divided into at least 2 portions.

As indicated, air separation unit 102, and the associated compression equipment, which may be, for example, electrical, gas turbine powered, or steam turbine powered, are land based and at a safe distance from the remainder of the facility. High-pressure gaseous nitrogen stream 103, high-pressure gaseous oxygen stream 106, and high-pressure natural gas stream 109, are thus delivered at sufficiently high pressure for the platform liquefaction process.

As used herein, the term “high-pressure gaseous nitrogen” is defined as having a delivery pressure to the offshore platform of between 40 bara and 100 bara, preferably 60 to 80 bara. As used herein, the term “high-pressure gaseous oxygen” is defined as having a delivery pressure to the offshore platform of between 40 bara and 100 bara, preferably 60 to 80 bara. As used herein, the term “high-pressure natural gas” is defined as having a delivery pressure to the offshore platform of between 30 bara and 700 bara, preferably 40 to 60 bara. As used herein, the term “natural gas” is presumed to be equivalent to “gaseous methane” or “hydrocarbon”. A used herein, the term “a safe distance” is defined as being greater than 1 mile, preferably greater than 5 miles.

First portion 104 is introduced into first liquefying heat exchanger 112, and second portion 105 is introduced into second liquefying heat exchanger 113. High-pressure gaseous oxygen stream 106 is divided into at least 2 portions. First portion 107 is introduced into first liquefying heat exchanger 112, and second portion 108 is introduced into second liquefying heat exchanger 113. Natural gas feed stream 109 is divided into at least 2 portions. First portion 110 is introduced into first liquefying heat exchanger 112, and second portion 111 is introduced into second liquefying heat exchanger 113.

First liquefying heat exchanger 112 outputs at least four streams; first liquefied nitrogen stream 114, first liquefied oxygen stream 118, first liquefied natural gas stream 122, first nitrogen vent stream 126, and possibly third nitrogen vent steam 128. Second liquefying heat exchanger 113 outputs at least four streams; second liquefied nitrogen stream 115, second liquefied oxygen stream 119, second liquefied natural gas stream 123, second nitrogen vent stream 127, and possibly fourth nitrogen vent stream 129. First liquefied nitrogen stream 114 and second liquefied nitrogen stream 115 are combined to form combined liquefied nitrogen stream 116, which is introduced into liquefied nitrogen storage 117. First liquefied oxygen stream 118 and second liquefied oxygen stream 119 are combined to form combined liquefied oxygen stream 120, which is introduced into liquefied oxygen storage 121. First liquefied natural gas stream 122 and second liquefied natural gas stream 123 are combined to form combined liquefied natural gas stream 124, which is introduced into liquefied natural gas storage 125.

Turning to FIG. 2, a detailed description of one embodiment of first liquefying heat exchanger 112 is provided. The skilled artisan will recognize that these details apply to single train or multiple train installations.

First portion 104 of high-pressure gaseous nitrogen stream 103, is introduced into first liquefying heat exchanger 112, wherein it is cooled, and forms cooled high-pressure nitrogen stream 201. Cooled high-pressure nitrogen stream 201 is then introduced into high-pressure nitrogen expansion turbine 202, wherein it cools by means of mechanical Turbo-expansion, thereby producing low-pressure nitrogen stream 203. Low-pressure nitrogen stream 203 is then re-introduced into first liquefying heat exchanger 112, wherein it exchanges heat with first portion 104 of high-pressure gaseous nitrogen stream 103 and first portion 107 of high-pressure gaseous oxygen stream 106. This produces first nitrogen vent stream 126 and first liquefied oxygen stream 118.

Turning to FIG. 3, a detailed description of another embodiment of first liquefying heat exchanger 112 is provided. As above, the skilled artisan will recognize that these details apply to single train or multiple train installations.

First portion 104 of high-pressure gaseous nitrogen stream 103, is introduced into first liquefying heat exchanger 112, wherein it is cooled, and forms cooled first fraction 301 and cooled second fraction 302. Cooled first fraction 301 is then introduced into first high-pressure nitrogen expansion turbine 303, wherein it cools by means of mechanical Turbo-expansion, thereby producing first low-pressure nitrogen stream 304. First low-pressure nitrogen stream 304 is then re-introduced into first liquefying heat exchanger 112, thereby producing warmed first low-pressure nitrogen stream 305. At least portion of warmed first low-pressure nitrogen stream 305 may be removed from the system as third nitrogen vent stream 128 (the equivalent stream for the second train would be fourth nitrogen vent stream 129). Warmed first low-pressure nitrogen stream 305 is then introduced into nitrogen compressor 306, thereby forming hot compressed nitrogen stream 307. Hot compressed nitrogen stream 307 is cooled in nitrogen after-cooler 308, thereby forming cooled compressed nitrogen stream 309.

Cooled second fraction 302 is reduced in pressure across expansion valve 310 wherein it cools by means of Joule-Thompson expansion, thus producing two-phase nitrogen stream 311. Two-phase nitrogen stream 311 is then introduced into phase separator 312, which produces liquid stream 313 and vapor stream 314. Liquid stream 313 is introduced into first liquefying heat exchanger 112, thereby producing vapor stream 315, which is re-introduced into phase separator 312. This passive heat exchange process relying on natural convection and requiring no pump is also known as thermosiphon.

Cooled compressed nitrogen stream 309 is reintroduced into first liquefying heat exchanger 112, thereby forming cold compressed nitrogen stream 316. Cold compressed nitrogen stream 316 is introduced into second high-pressure nitrogen expansion turbine 317, wherein it is cooled by means of mechanical turbo-expansion, thereby producing second low-pressure nitrogen stream 318. Second low-pressure nitrogen stream 318 is combined with vapor stream 314, thereby forming combined waste nitrogen stream 319. Combined waste nitrogen stream 319 is introduced into first liquefying heat exchanger 112, thereby forming first nitrogen vent stream 126.

First portion 107, of high-pressure gaseous oxygen stream 106, is introduced into first liquefying heat exchanger 112, thereby forming first liquefied oxygen stream 118. First portion 110, natural gas feed stream 109, is introduced into first liquefying heat exchanger 112, thereby forming first liquefied natural gas stream 122.

One of ordinary skill in the art will recognize that the nitrogen liquefaction processes disclosed in FIG. 2 and FIG. 3, as described herein, are once through nitrogen refrigeration processes. There is no nitrogen recycle to any compression step. After exchanging heat with the oxygen or natural gas, the nitrogen is vented.

Turning to FIG. 4, one non-limiting embodiment of an air separation unit with liquid oxygen pumping is provided. Inlet air stream 401 is cooled by indirect heat exchange with high-pressure liquid oxygen stream 412, and compressed cool feed air stream 404, thus producing cool inlet air stream 402. At least a portion of the cool inlet air stream 402 is introduced into a cold booster 403, thereby producing the compressed cool feed air stream 404. At least a first portion 405 is introduced into an expander 407, thereby producing an expanded feed air stream 408. Expanded feed air stream 408 is introduced into air separation column 409. In one embodiment of the present invention, the cold booster 403 and expander 407 are connected by a common drive shaft. A second portion is further cooled, thereby producing the cold feed air stream 406 which then enters air separation unit column 409. Liquid oxygen stream 410 from air separation unit column 409 is pressurized in liquid oxygen pump 411, thus producing high-pressure liquid oxygen stream 412. High-pressure liquid oxygen stream 412 is then heated by indirect heat exchange with inlet air stream 401, thus producing high-pressure gaseous oxygen stream 414.

Stream 414 may be sent directly to the liquefaction system where is liquefied. Alternatively, stream 414 may be “densified” as supercritical fluids are not technically liquefied. Critical pressure of nitrogen is 34 bara and critical pressure of oxygen is 50.4 bara. Alternatively, stream 414 may be further compressed with a gaseous oxygen compressor before being sent to the liquefaction system and liquefied. Alternatively, oxygen gas may exit distillation 409 at low pressure, warmed in exchanger 413, and then compressed form low to high pressure in a gaseous compressor.

Similarly, nitrogen may be withdrawn from distillation 409 as either liquid or vapor, warmed and/or vaporized in exchanger 413, compressed by liquid pumping or gaseous compression to deliver high pressure nitrogen to the liquefaction system.

It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above. 

What is claimed is:
 1. A process for producing liquid oxygen, comprising an offshore platform comprising: a) cooling a high-pressure nitrogen gas stream in a main heat exchanger, thereby producing a cooled high-pressure nitrogen gas stream, b) expanding the cooled high-pressure nitrogen gas stream in a turbo-expander, thereby producing a cold low-pressure nitrogen gas stream, c) warming the cold low-pressure nitrogen gas stream by indirect heat exchange with a high-pressure gaseous oxygen stream, thereby producing a liquefied oxygen stream and a warm low-pressure nitrogen gas stream, wherein, at least a portion of the warm low-pressure nitrogen gas stream is vented to the atmosphere.
 2. The process of claim 1, wherein step b) further comprises: i. expanding the cooled high-pressure nitrogen stream in a first turbo-expander, thus producing a first low pressure nitrogen stream, ii. compressing the first low-pressure nitrogen stream in a nitrogen compressor, thereby producing a hot compressed nitrogen stream, iii. cooling the hot compressed nitrogen stream in a nitrogen after-cooler, thereby producing a cooled compressed nitrogen stream, and iv. expanding the cooled compressed nitrogen stream in a second turbo-expander, thus producing the cold low-pressure nitrogen gas stream.
 3. The process of claim 2, wherein the nitrogen compressor of step ii is driven by one or both of the expanders of steps i and/or iv.
 4. The process of claim 2, wherein at least a portion of the warm low-pressure nitrogen gas is vented to the atmosphere at the end of step
 1. 5. The process of claim 1, wherein the high-pressure nitrogen gas stream has a pressure of greater than 40 bara.
 6. The process of claim 1, wherein the high-pressure nitrogen gas stream has a pressure of greater than 60 bara.
 7. The process of claim 1, wherein step c) further comprises: warming the cold low-pressure nitrogen gas stream by indirect heat exchange with both: i. a high-pressure gaseous oxygen stream, thereby producing a liquefied oxygen stream, ii. a hydrocarbon comprising stream, thereby producing a liquefied hydrocarbon comprising stream, and iii. producing a warm low-pressure nitrogen gas stream.
 8. The process of claim 1, further comprising an air separation unit, wherein the high-pressure nitrogen stream and the high-pressure oxygen stream are produced by the air separation unit.
 9. The process of claim 8, wherein the distance between the air separation unit and the offshore platform is greater than 1 mile.
 10. The process of claim 8, wherein the distance between the air separation unit and the offshore platform is greater than 5 miles.
 11. The process of claim 8, wherein the air separation unit comprises a liquid oxygen pump and a main heat exchanger, and wherein a liquid oxygen stream is compressed in the liquid oxygen pump and vaporized in the main heat exchanger, thereby producing the high-pressure gaseous oxygen stream.
 12. The process of claim 8, wherein, the nitrogen and/or oxygen from the air separation unit are compressed by gaseous mechanical compression. 